Piezoelectric ink jet print head and method of making the same

ABSTRACT

An ink jet print head includes a cavity plate having a plurality of nozzles and a plurality of pressure chambers communicating with the respective nozzles, and a plate-like piezoelectric actuator, in which piezoelectric sheets having a plurality of electrodes formed at positions with respect to the pressure chambers are stacked one after another. The piezoelectric actuator is bonded to the cavity plate so as to close the pressure chambers in the cavity plate. Each of the piezoelectric sheets has a thickness of between 5-40 μm, preferably between 15-30 μm. Surface electrodes, which electrically connect one of the electrodes, are provided at both end portions of a surface of the piezoelectric actuator, which is opposed to a surface to be bonded to the cavity plate. Protrusions having a thickness of the surface electrodes are provided between the surface electrodes on the surface of the piezoelectric actuator.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The invention relates to a piezoelectric ink jet print head, moreparticularly, to an ink jet print head using a laminated piezoelectricactuator and a method of fabricating the same.

[0003] 2. Description of Related Art

[0004] Conventionally, an ink jet print head using a laminatedpiezoelectric actuator has been known.

[0005] As shown in FIG. 32, an ink jet print head 300 includes a cavityplate 310 formed by stacking substantially rectangular metal plates, inwhich a plurality of pressure chambers 316, which extend in a directionperpendicular to a longitudinal direction of the cavity plate 310, areformed so as to be aligned in parallel with the longitudinal directionof the cavity plate 310. A plate-like piezoelectric actuator 320 havinga substantially rectangular plate shape is bonded to the cavity plate110 so as to close the pressure chambers 316. A flat flexible cable 330for connecting with external equipment is bonded on the piezoelectricactuator 320.

[0006] As shown in FIGS. 32 and 33, a plurality of surface electrodes326, 327 are provided on the piezoelectric actuator 320 at its surfaceopposite to the surface to be bonded to the cavity plate 310 (an uppersurface of the plate-type piezoelectric actuator 320 in FIG. 32). Thesurface electrodes 326 and 327 are formed on both sides and areconnected with driving electrodes and common electrodes, respectively.An oval ink supply hole 319 is provided at a left end portion of thecavity plate 310.

[0007] According to the conventional piezoelectric actuator, if thepiezoelectric sheet is too thin, metallic material in internalelectrodes may be diffused too much during sintering of thepiezoelectric sheet. This results in piezoelectric characteristic of thepiezoelectric sheet being spoiled.

[0008] On the other hand, if the piezoelectric sheet is too thick,restraint of non-active portions have a great effect on active portions.Accordingly, the active portions cannot sufficiently deform.

[0009] Further, if the internal electrode is too thin, the electrodebecomes too narrow or is cut off due to the diffusion of the metallicmaterial during sintering of the piezoelectric sheet. On the other hand,if the internal electrode is too thick, delamination frequently occursin an interface between portions having the internal electrodes andportions not having the internal electrodes, because there is a greatdifference in the thickness of the piezoelectric sheets afterlamination.

[0010] Referring to FIGS. 34 and 35, adhesion of the plate-likepiezoelectric actuator 320 onto the cavity plate 310 in the ink jetprint head 300 structured as described above will be described. First,as shown in FIG. 34, the cavity plate 310 is placed on a workbench 370having a flat surface. Next, the piezoelectric actuator 320, to which anadhesive is applied at its bottom, is placed on the cavity plate 310 onthe workbench 370, while checking to make sure that the cavity plate 310is in proper alignment with the piezoelectric actuator 320. Then, asshown in FIG. 35, a force of 10 kg-weight is applied to the uppersurface of the piezoelectric actuator 320, in a direction indicated withan arrow A, using an assembly jig 340 having a flat bottom surface.Thus, the piezoelectric actuator 320 is bonded to the cavity plate 310.

[0011] However, in the above-described method of adhering the plate-likepiezoelectric actuator 320 to the cavity plate 310, the assembly jig 340only presses the surface electrodes 326, 327 provided on the surface ofthe piezoelectric actuator 320. As shown in FIGS. 34 and 35, when thereare waves 320 a, which are smaller than the thickness of the surfaceelectrodes 326, 327, in a middle of the piezoelectric actuator 320, thewaves 320 a cannot be flatted using the assembly jig 340. If the waves320 a remain in the piezoelectric actuator 320, an adhesion failure mayoccur in the piezoelectric actuator 320 and the cavity plate 310. Inkleakage may also occur.

[0012] The piezoelectric ink jet print head as described above istypically produced by the following method. First, internal electrodesare screen-printed on piezoelectric sheets, and the piezoelectric sheetshaving the electrodes and the piezoelectric sheets not having theelectrodes are alternatively stacked. The laminated piezoelectric sheetsare pressed and sintered. After that, a deformation restraining memberis bonded to the laminated piezoelectric sheets using an adhesive.

[0013] Further, the piezoelectric actuator fabricated as described aboveis bonded to the cavity plate having pressure chambers. Finally, thepiezoelectric ink jet print head is obtained.

[0014] When the piezoelectric actuator is fabricated using such aconventional method, asperities are developed in the surfaces of thepiezoelectric actuator and the cavity plate, which are adhered eachother, after sintering of the piezoelectric sheets. As a result, anadhesion failure may occur in the piezoelectric actuator and the cavityplate.

[0015] Accordingly, grinding is required to be performed on the surfaceof the piezoelectric actuator after sintering. All of the above lead toproblems in operating efficiency and costs in the production and use ofpiezoelectric ink jet printheads.

SUMMARY OF THE INVENTION

[0016] In light of the foregoing, it would be desirable to provide apiezoelectric ink jet print head using a laminated piezoelectricactuator that addresses the foregoing drawbacks associated with otherknown piezoelectric ink jet print heads.

[0017] One aspect of the invention involves a piezoelectric print headthat includes a cavity plate and a plate-like piezoelectric actuator.The cavity plate includes a plurality of nozzles and a plurality ofpressure chambers communicating with the respective nozzles. Theplate-like piezoelectric actuator is formed into a single laminatedstructure by laminating a plurality of piezoelectric sheets including aplurality of electrodes which are formed at positions so as to bealigned with the respective pressure chambers. The laminatedpiezoelectric actuator is then sintered and bonded to the cavity plateso as to close the pressure chambers provided in the cavity plate. Inthe piezoelectric ink jet print head, each of the piezoelectric sheetshas a thickness of between 5-40 μm, preferably between 15-30 μm.

[0018] According to another aspect of the invention, a piezoelectric inkjet print head includes a cavity plate, a plate-like piezoelectricactuator, surface electrodes and protrusions. The cavity plate includesa plurality of nozzles and a plurality of pressure chamberscommunicating with the respective nozzles. The plate-like piezoelectricactuator is formed into a single laminated structure by laminating aplurality of piezoelectric sheets including a plurality of electrodeswhich are formed at positions so as to be aligned with the respectivepressure chambers. The laminated piezoelectric actuator is then sinteredand bonded to the cavity plate so as to close the pressure chambersprovided in the cavity plate. The surface electrodes are provided at anend portion of a surface of the piezoelectric actuator, which is opposedto a surface of the piezoelectric actuator to be bonded to the cavityplate, and are electrically connected with the plurality of electrodes.Each of the protrusions has a thickness of the surface electrodes and isprovided on the surface of the piezoelectric actuator where the surfaceelectrodes are provided.

[0019] According to yet another aspect of the invention, a piezoelectricink jet print head includes a cavity plate and a plate-likepiezoelectric actuator. The cavity plate includes a plurality of nozzlesand a plurality of pressure chambers communicating with the respectivenozzles. The plate-like piezoelectric actuator is formed into a singlelaminated structure by laminating a plurality of piezoelectric sheetsincluding a plurality of electrodes which are formed at positions so asto be aligned with the respective pressure chambers. The laminatedpiezoelectric actuator is then sintered and bonded to the cavity plateso as to close the pressure chambers provided in the cavity plate. Thepiezoelectric actuator has a flatness of 30 μm or less, which is adifference of height between projections and depressions formed on thepiezoelectric actuator at its surface to which the cavity plate isbonded.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Various exemplary embodiments of the invention will be describedin detail with reference to the following figures wherein:

[0021]FIG. 1 is a perspective view of essential parts of an ink jetprinter, in which a piezoelectric ink jet print head of the invention isused;

[0022]FIG. 2 is a sectional view of essential parts of the piezoelectricink jet print head of a first embodiment of the invention;

[0023]FIG. 3 is an electric connection or wiring diagram of apiezoelectric actuator of the piezoelectric ink jet print head of FIG.2;

[0024]FIG. 4 is a graph showing relationships between a thickness of apiezoelectric sheet and a voltage constant and between the thickness ofthe piezoelectric sheet and an amount of deformation of thepiezoelectric sheet, in the piezoelectric actuator in the piezoelectricink jet print head of FIG. 2;

[0025]FIG. 5 is a graph showing relationships between a thickness of aninternal electrode and a capacitance, in the piezoelectric actuator inthe piezoelectric ink jet print head of FIG. 2;

[0026]FIG. 6 is a disassembled perspective view of the piezoelectricactuator, showing a structure of an active layer and a restraininglayer;

[0027]FIG. 7 is a disassembled perspective view of essential parts ofthe piezoelectric ink jet print head of FIG. 2;

[0028]FIG. 8 is a sectional view of a modification of a piezoelectricactuator to be used in the piezoelectric ink jet print head of FIG. 2;

[0029]FIG. 9 is a sectional view of another modification of apiezoelectric actuator to be used in the piezoelectric ink jet printhead of FIG. 2;

[0030]FIG. 10 is a disassembled perspective view of an ink jet printhead of a second embodiment of the invention;

[0031]FIG. 11 is a plan view of a plate-like piezoelectric actuator tobe used in the ink jet print head of FIG. 10;

[0032]FIG. 12 is a perspective view of the plate-like piezoelectricactuator and a cavity plate, wherein the piezoelectric actuator isseparated from the cavity plate;

[0033]FIG. 13 is a disassembled perspective view of the plate-likepiezoelectric actuator;

[0034]FIG. 14 is a sectional view of the plate-like piezoelectricactuator taken along line I-I in FIG. 12, looking in the direction ofthe appended arrows;

[0035]FIG. 15 is a disassembled perspective view of the cavity plate;

[0036]FIG. 16 a disassembled sectional view of the cavity plate takenalong line II-II in FIG. 15, looking in the direction of the appendedarrows;

[0037]FIG. 17 is a diagram showing a process of adhering the plate-likepiezoelectric actuator to the cavity plate;

[0038]FIG. 18 is a diagram showing the process of adhering theplate-like piezoelectric actuator to the cavity plate;

[0039]FIG. 19 is a diagram showing the process of adhering theplate-like piezoelectric actuator to the cavity plate;

[0040]FIG. 20 is a sectional view showing a state where the plate-likepiezoelectric actuator is adhered to the cavity plate;

[0041]FIG. 21 is a perspective view of a piezoelectric ink jet head of athird embodiment of the invention, with its nozzles facing upward;

[0042]FIG. 22 is a disassembled perspective view of the piezoelectricink jet head of FIG. 21;

[0043]FIG. 23 is a disassembled perspective view of the piezoelectricink jet head of FIG. 21, looking down from a frame;

[0044]FIG. 24 is a bottom view of a bottom plate of the frame of thepiezoelectric ink jet head of FIG. 21;

[0045]FIG. 25 is a perspective view of a front head unit in thepiezoelectric ink jet head of FIG. 21;

[0046]FIG. 26 is a sectional view of the front head unit in thepiezoelectric ink jet head of FIG. 21;

[0047]FIG. 27 is a disassembled perspective view of a cavity plate inthe piezoelectric ink jet head of FIG. 21;

[0048]FIG. 28 is a disassembled enlarged perspective view of the cavityplate in the piezoelectric ink jet head of FIG. 21;

[0049]FIG. 29 is a disassembled enlarged perspective view of apiezoelectric actuator in the piezoelectric ink jet head of FIG. 21;

[0050]FIG. 30A is a three-dimensional view showing a surface of onesample of the piezoelectric actuator, wherein the surface is dividedinto 208 (8×26) sections;

[0051]FIG. 30B shows a three-dimensional surface profiling data viewedfrom an ODD side shown in FIG. 30A;

[0052]FIG. 31A is a line graph showing inclination of the surface in alateral direction, by eight sections, in FIG. 30A;

[0053]FIG. 31B is a line graph showing inclination of the surface in alongitudinal direction, by 26 sections, in FIG. 30A;

[0054]FIG. 32 is a disassembled perspective view of a conventional inkjet print head;

[0055]FIG. 33 is a plan view of a conventional plate-like piezoelectricactuator;

[0056]FIG. 34 is a diagram showing a process of adhering theconventional plate-like piezoelectric actuator to the cavity plate 110;and

[0057]FIG. 35 is a diagram showing the process of adhering theplate-like piezoelectric actuator to the cavity plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0058] Various exemplary embodiments of the invention will be describedwith reference to the accompanying drawings.

[0059] A first embodiment of the invention will be described withreference to FIGS. 1 to 8.

[0060] With reference to FIG. 1, the ink jet printer 1 includes ahorizontal platen 10 for feeding a sheet 11 perpendicularly to its axis.The platen 10 includes a shaft 12, which is rotatably supported by aframe 13, and can be rotated by a motor 14 via a drive gear train. Apiezoelectric ink jet print head 15 is provided to be opposed to theplaten 10.

[0061] The piezoelectric ink jet print head 15 is disposed on a carriage18 with an ink supply device 16. A pair of guide rods 20 (20 a and 20 b)extend below the platen 10 and in parallel to its shaft 12, and arefixed to the frame 13. The guide rods 20 slidably support the carriage18, which is connected to a timing belt 24. The timing belt 24 extendsbetween a driven pulley 21 and a driving pulley 22, which can be rotatedby a motor 23 to drive the timing belt 24. Thus, the timing belt 24 canslide the carriage 18 on the guide rods 20 along the platen 10, with thepiezoelectric ink jet print head 15 facing the platen 10.

[0062] The piezoelectric ink jet print head 15 includes a cavity plate30 and a piezoelectric actuator 3, which consists of an active layer 38and a restraining layer 70. The cavity plate 30 has three ink channels32 a, 32 b, 32 c formed therein and each having an open top. The inkchannels 32 a, 32 b, 32 c function as an ink chamber. The cavity plate30 also has three orifices 37 a, 37 b, 37 c formed through its bottomand communicating with the ink channels 32 a, 32 b and 32 c,respectively.

[0063] The active layer 38 lies on the top of the cavity plate 30. Theactive layer 38 includes six piezoelectric sheets 40 a, 40 b, 40 c, 40d, 40 e, 40 f laminated or stacked together and each having an electrodepattern formed on their upper sides. The piezoelectric sheets 40 a to 40f each have an electrostrictive effect. The electrostrictive effect ofthe active layer 38 changes the volume of the ink channels 32 a, 32 b,32 c to eject through the orifices 37 a, 37 b, 37 c, respectively, theink stored in these channels. The restraining layer 70 lies on the topof the active layer 38 and is formed integrally with the active layer38. The restraining layer 70 includes three piezoelectric sheets 71 a,71 b, 71 c laminated or stacked together. The restraining layer 70restrains the active layer 38 from deforming upward when the activelayer 38 is driven. The restraining layer 70 makes the wholepiezoelectric actuator 3 more rigid to prevent cross talk.

[0064] As shown in FIG. 7, the cavity plate 30 includes a channel body34, which is formed in a rectangular parallelepiped. In the channel body34, the ink channels 32 a, 32 b, 32 c are formed in parallel and spacedat regular intervals. Each of the ink channels 32 a, 32 b, 32 c has awidth of about 250 μm and a height of 60 μm. On the bottom of thechannel body 34, an orifice plate 36 is disposed so as to cover itsbottom. The orifice plate 36 is formed with orifices 37 so as to bealigned with the respective ink channels 32 a, 32 b, 32 c for ejectingthe ink. The channel body 34 and the orifice plate 36 are made of ironmaterial, for example, and bonded together though other materials couldbe used. For example, the channel body 34 and orifice plate 36 might beintegrally molded by sintering ceramics or the like, orinjection-molding alumina or similar material. Each of the ink channels32 a, 32 b, 32 c is always filled with ink by being supplied through asupply passage (not shown) communicating with the ink supply device 16(see FIG. 8).

[0065] A negative pressure is applied to the ink in the ink channels 32a, 32 b, 32 c so that the surface tension of ink outwardly producesconcave menisci of ink in the orifices 37 a, 37 b, 37 c. This normallyprevents ink from leaking through the orifices 37 a, 37 b, 37 c, butallows ink to be ejected through them only when the internal pressure inthe ink channels 32 a, 32 b, 32 c rises. The orifices 37 a, 37 b, 37 cmight be replaced by nozzles extending from the respective ink channels32 a, 32 b, 32 c. The nozzles could be angled to adjust the direction ofink ejection from the ink channels 32 a, 32 b, 32 c. The orifices 37 a,37 b, 37 c might be positioned elsewhere than the bottoms of the inkchannels 32 a, 32 b, 32 c.

[0066] As shown in FIG. 6, each of the three piezoelectric sheets 40 a,40 c, 40 e of the active layer 38 has an internal negative electrode 42and a connector 43 which are formed on its upper side as stated lateron. The connector 43 connects the negative electrode 42 electrically tothe outside. The negative electrode 42 covers the substantial portionexcept a peripheral portion of the upper side of the associatedpiezoelectric sheet 40 a, 40 c or 40 e. Likewise, each of the otherthree piezoelectric sheets 40 b, 40 d, 40 f of the active layer 38 hasthree internal positive electrodes 44 a, 44 b, 44 c and three connectors45 a, 45 b, 45 c formed on its upper side. The connectors 45 a, 45 b, 45c electrically connect the internal positive electrodes 44 a, 44 b, 44c, respectively, to the outside. The internal positive electrodes 44 a,44 b, 44 c are associated with the ink channels 32 a, 32 b, 32 c (FIG.7), respectively, and extend in parallel. Each of the internal positiveelectrodes 44 a, 44 b, 44 c takes the form of a belt or band and has awidth of about 120 μm. When designing the ink jet print head, a pitch ofthe channels affect the width of the internal positive electrodes as thedriving electrode. In other words, the width of the pressure chamber inthe cavity plate determines the width of the driving electrodes. It ispreferable to set a width of the driving electrodes to 40-70% of thewidth of the pressure chamber. If it is narrower than 40% of the widthof the pressure chamber, enough pressure changes are not obtained withrespect to the volume of the pressure chamber. This may cause unstableink ejection. On the contrary, if it is wider than 70% of the width ofthe pressure chamber, the deformation of the piezoelectric sheet may berestricted due to the contact area between the electrode and the cavitybeam. This would not increase the pressure change. But this may cause acrosstalk of the pressure changes among the neighboring channels. On theother hand, when considering the design of the ink jet print head, it ispreferable to set the resolution of the ink head, which is a pitch ofthe channels, to 85 μm corresponding to 300 dpi, to 847 μm correspondingto 30 dpi, more preferably to 169 μm corresponding to 150 dpi, or to 508μm corresponding to 50 dpi. When it is set to a narrower pitch of under85 μm, the width of the beam is required to be between about 10-20 μmwhich does not provide enough area to contact with the electrode. Whenit is set to a wider pitch of over 847 μm, the frequency or number ofscans of the ink head becomes too high to obtain a fine print quality.This may result in the ink jet printer not operating any more.Therefore, based on the resolution of the ink jet print head andconsidering the beam width and the efficiency of the pressure changes,the width of the driving electrodes is set to between 50-500 μm,preferably between 80-200 μm. In addition, because the electrodes areformed by screen printing a paste made of Ag-Pd metallic material ontothe piezoelectric sheet, it would be difficult to form lines narrowerthan 50 μm. Therefore, it is preferable to form lines which are widerthan 80 μm.

[0067] The internal negative electrode 42 and the positive electrodes 44a, 44 b, 44 c are also made of Ag-Pd metallic material and each have athickness of about between 0.7-5 m, preferably between 1-3 μm.

[0068] The piezoelectric sheets 40 a-40 f with the two types ofelectrode patterns printed on them are alternately laminated or stacked.

[0069] Thus, as shown in FIG. 2, one internal negative electrode 42 ispositioned on one side of each of the piezoelectric sheets 40 a, 40 c,40 e, while three internal positive electrodes 44 a, 44 b, 44 c arepositioned on one side of each of the piezoelectric sheets 40 b, 40 d,40 f. Each of the six piezoelectric ceramic sheets 40 a to 40 f consistsof piezo-electrically active portions 46 a, 46 b, 46 c andpiezo-electrically inactive portions 48. Each of the active portions 46a, 46 b, 46 c of the five sheets 40 a to 40 e is formed between theadjacent negative electrode 42 and one of the adjacent positiveelectrodes 44 a, 44 b, 44 c, each of which takes the form of a belt orband. Each of the active portions 46 a, 46 b, 46 c of the bottom sheet40 f is formed under one of the adjacent positive electrodes 44 a, 44 b,44 c. Each of the active portions 46 a, 46 b, 46 c has a width of about120 μm. The other portions of the six piezoelectric sheets 40 a to 40 fare the inactive portions 48. When voltage is applied between thepositive electrodes 44 a, 44 b or 44 c and the negative electrodes 42,electric fields are generated in the associated active portions 46 a, 46b or 46 c, which then deform vertically due to the electrostrictiveeffect, while no electric field is generated in the inactive portions48, which do not deform. The channel body 34 is fixed to the bottom ofthe active layer 38 in such a manner that the active portions 46 a, 46b, 46 c are positioned over or above the ink channels 32 a, 32 b, 32 c,respectively.

[0070] The restraining layer 70 includes three piezoelectric sheets 71a, 71 b, 71 c, which are identical in structure and material and equalin size to the piezoelectric sheets 40 a to 40 f of the active layer 38.As shown in FIGS. 2, 3 and 6, each of the top and bottom piezoelectricsheets 71 a and 71 c of the restraining layer 70 has three dummypositive electrodes 73 a, 73 b, 73 c and three connectors 75 a, 75 b, 75c, which are identical in structure to the internal positive electrodes44 a, 44 b, 44 c and the connectors 45 a, 45 b, 45 c, respectively, onthe piezoelectric sheets 40 b, 40 d, 40 f. The middle piezoelectricsheet 71 b of the restraining layer 70 has a dummy negative electrode 72and a connector 74, which are identical in structure to the internalnegative electrodes 42 and the connectors 43, respectively, on thepiezoelectric sheets 40 a, 40 c, 40 e.

[0071] The active layer 38 and the restraining layer 70 are produced bythe following method. First, ceramic powder of ferroelectric leadzirconate titanate (PZT (PbTiO₃·PbZrO₃)) material, a binder and asolvent are mixed into a mixed liquid having a viscosity between 10,000and 30,000 CPS. The mixed liquid is spread and dried on films ofpolyethylene terephthalate (PET) or other plastic material to formpiezoelectric sheets.

[0072] In the embodiment, each of the piezoelectric sheets has athickness of between 5-40 μm, preferably between 15-30 μm.

[0073] Metallic material is screen-printed on those portions of five ofthe piezoelectric sheets which will be the internal positive electrodes44 a, 44 b, 44 c, the dummy positive electrodes 73 a, 73 b, 73 c and theconnectors 45 a, 45 b, 45 c, 75 a, 75 b, 75 c. These sheets will be thepiezoelectric sheets 40 b, 40 d, 40 f, 71 a, 71 c. Likewise, metallicmaterial is screen-printed on those portions of the other four of thepiezoelectric sheets which will be the internal negative electrodes 42,the dummy negative electrode 72 and the connectors 43, 74. These sheetswill be the piezoelectric sheets 40 a, 40 c, 40 e, 71 b.

[0074] The nine piezoelectric sheets 40 f, 40 e, 40 d, 40 c, 40 b, 40 a,71 c, 71 b, 71 a are stacked one after another, in this order, frombelow upward, with the piezoelectric sheet 40 f positioned at thebottom. At this stage, the active layer 38 and the restraining layer 70are not yet distinguished.

[0075] The stacked piezoelectric sheets are pressed with heat, degreasedand sintered to form a piezoelectric ceramic block, which consists ofthe active layer 38 and restraining layer 70.

[0076] The sintering of the piezoelectric sheets stacked as a laminatedblock will be explained below.

[0077] As stated already, the piezoelectric actuator 3 consists of anactive layer 38 and a restraining layer 70. Electrodes are essential tothe active layer 38, while the restraining layer 70 functionally needsto have no electrode. When the laminated block is sintered, however, thepiezoelectric ceramics differ in shrinking percentage from the metallicmaterial for the electrodes. Even a slight difference in shrinkingpercentage may warp or wave the sintered active layer 38, therebydamaging or spoiling its flatness. The non-flat active layer 38 can bebonded less closely (with lower adherence) to the cavity plate 30. Thismay cause a problem that ink leaks from the ink channels 32 a, 32 b, 32c, so that defective products may be produced. This may also cause aproblem that the active layer 38 needs regrinding (or needs to be groundagain), so that the number of producing process steps may increase andthe production costs may be higher. Non-flat active layer 38 may furthercause a problem that gaps between the active layer 38 and the cavityplate 30 need filling with fillers, which may reduce the strength of thelaminated block.

[0078] Therefore, as stated earlier, the restraining layer 70 and theactive layer 38 are made of the same piezoelectric ceramic material sothat they are equal in shrinking percentage when the ceramics aresintered. The dummy negative electrode 72, the connector 74, the dummypositive electrodes 73 a, 73 b, 73 c and the connectors 75 a, 75 b, 75c, which are formed on the ceramic sheets 71 a, 71 b, 71 c of therestraining layer 70, are identical to the internal negative electrodes42, the connectors 43, the internal positive electrodes 44 a, 44 b, 44 cand the connectors 45 a, 45 b, 45 c, respectively, on the piezoelectricceramic sheets 40 a to 40 f of the active layer 38, but do notcontribute to deformation of the restraining layer 70. Therefore,because the active layer 38 and the restraining layer 70 have the verysame structure, they can be identical in shrinking percentage when theyare sintered. The internal electrodes 42, 44 a, 44 b, 44 c, 72, 73 a, 73b, 73 c and the connectors 43, 45 a, 45 b, 45 c, 74, 75 a, 75 b, 75 c ofthe active and restraining layers 38, 70 of the laminated block as awhole are arrayed in vertical symmetry (symmetrically in the directionsof lamination). This symmetrizes the shrinking percentage of the wholelaminated block so as not to warp this block being sintered.

[0079] As shown in FIG. 3, the piezoelectric actuator 3 includes anexternal negative electrode 52 a made of electrically conductivemetallic material. This external electrode 52 a electrically connectsthe connectors 43 on the three piezoelectric sheets 40 a, 40 c, 40 e andthe connector 74 on the piezoelectric sheet 71 b. The piezoelectricactuator 3 includes another external negative electrode 52 b made of anelectrically conductive metal plate. This external electrode 52 belectrically connects the connectors 75 a, 75 b, 75 c on thepiezoelectric sheets 71 a, 71 c. These external electrodes 52 a and 52 bare electrically connected. Consequently, the dummy electrodes 72, 73 a,73 b, 73 c on the piezoelectric sheets 71 a, 71 b, 71 c and the internalnegative electrodes 42 on the piezoelectric ceramic sheets 40 a, 40 c,40 e are equal in electric potential.

[0080] The piezoelectric actuator 3 also includes three externalpositive electrode 54 a, 54 b, 54 c made of electrically conductivemetallic material. The external electrode 54 a electrically connects theconnectors 45 a on the piezoelectric sheets 40 b, 40 d, 40 f. Theexternal electrode 54 b electrically connects the connectors 45 b on thepiezoelectric ceramic sheets 40 b, 40 d, 40 f. The external electrode 54c electrically connects the connectors 45 c on the piezoelectric ceramicsheets 40 b, 40 d, 40 f. The external negative electrodes 52 a, 52 b andthe positive electrodes 54 a, 54 b, 54 c are formed out of metallicmaterial, which is printed directly on side faces of the active layer 38and the restraining layer 70, or with which these faces are coateddirectly. Alternatively, the external electrodes might be metal platesconnected in contact with the connectors 43, 45 a, 45 b, 45 c, 74, 75 a,75 b, 75 c, or wires soldered to these connectors. These electrodesmight have other structures.

[0081] Because the dummy electrodes 72, 73 a, 73 b, 73 c do notcontribute to deformation of the piezoelectric sheets 71 a, 71 b, 71 cof the restraining layer 70, it is not necessary to apply a drivevoltage to these electrodes. Even if the dummy electrodes 72, 73 a, 73b, 73 c and the connectors 74, 75 a, 75 b, 75 c were insulated in ordernot to be electrically polarized, a potential difference might begenerated between them and the top internal negative electrode 42 of theactive layer 38. The potential difference produces an electric capacity,which produces an electric current. The current is so small as not tocontribute to deformation of the piezoelectric sheets 71 a, 71 b, 71 c,but results in a power loss. In particular, if the power source for thepiezoelectric actuator 3 is a battery, the power loss shortens the lifeof the battery. Therefore, the dummy electrodes 72, 73 a, 73 b, 73 c andthe connectors 74, 75 a, 75 b, 75 c are connected electrically to theinternal negative electrodes 42 of the active layer 38. This prevents apotential difference from being generated between the dummy electrodes72, 73 a, 73 b, 73 c and the connectors 74, 75 a, 75 b, 75 c of therestraining layer 70 and the top internal negative electrode 42 of theactive layer 38. It is consequently possible to prevent the productionof a needless capacity.

[0082] The laminated block thus constructed is then immersed in an oilbath (not shown) filled with a silicone oil or another insulating oil ata temperature of about 130° C. An electric field of about 2.5 kv/mm isapplied between the external negative electrode 52 a and the externalpositive electrodes 54 a, 54 b, 54 c to polarize the piezoelectricsheets 40 a, 40 b, 40 f of the active layer 38.

[0083] As shown in FIG. 3, the external negative electrode 52 a isgrounded via a cord (not shown) to have a ground potential. The externalpositive electrodes 54 a, 54 b, 54 c are connected to the positive poleof a power source 60, using a cord (not shown), via switches 62 a, 62 b,62 c, respectively. The negative pole of the power source 60 isgrounded. When a controller (not shown) makes one or more of theswitches 62 a, 62 b, 62 c closed, a drive voltage is applied between theassociated internal positive electrodes 44 a, 44 b, 44 c and theinternal negative electrodes 42 from the power source 60.

[0084] As shown in FIG. 7, the block consisting of the active layer 38and the restraining layer 70, and the cavity plate 30 are assembled intothe piezoelectric ink jet print head 15 (FIG. 2).

[0085]FIGS. 8 and 9 show modified piezoelectric actuators 3A and 3B,respectively. In FIGS. 8 and 9, parts identical to the counterparts ofthe piezoelectric actuator 3 are assigned the same reference numeralswithout being described.

[0086] With reference to FIG. 8, as is the case with the piezoelectricactuator 3, the modified piezoelectric actuator 3A consists of an activelayer 38A and a restraining layer 70A. The active layer 38A of thepiezoelectric actuator 3A includes four piezoelectric sheets 40. Therestraining layer 70A includes five piezoelectric sheets 71, on each ofwhich a dummy negative electrode 72 is formed. Each dummy negativeelectrode 72 is grounded through a ground electrode. As shown in FIG. 2,the active layer 38 of the piezoelectric actuator 3 includes sixpiezoelectric sheets 40 a to 40 f. The active layer 38A of thepiezoelectric element 3A differs from the active layer 38 in includingfour piezoelectric sheets 40. As shown in FIG. 6, the restraining layer70 of the piezoelectric actuator 3 includes the three piezoelectricsheets 71 a, 71 b, 71 c, which are alternately stacked and sintered. Asshown in FIG. 8, the restraining layer 70A of the piezoelectric actuator3A has five piezoelectric sheets 71, which are identical in structure tothe piezoelectric sheets 40 a, 40 b, 40 c, 71 b. The piezoelectricsheets 71 are stacked and sintered, and then the dummy electrodes 72 areformed thereon. The number of piezoelectric sheets 40 of the activelayer 38A and the number of piezoelectric sheets 71 of the restraininglayer 70A might vary under various conditions. If the shrinkingpercentage during sintering of the electrodes provided as the dummyelectrodes is within a certain range where the restraining layer 70 isprevented from warping, this restraining layer 70 could include only thepiezoelectric sheets that are identical in structure to thepiezoelectric sheets 40 a, 40 b, 40 c, 71 b.

[0087] With reference to FIG. 9, as is the case with the modifiedpiezoelectric actuator 3A, the modified piezoelectric actuator 3Bincludes an active layer 38B including four piezoelectric sheets 40. Thepiezoelectric actuator 3B also includes a restraining layer 70Bincluding five piezoelectric sheets, each of which has three dummypositive electrodes 73 a, 73 b, 73 c formed on it. The piezoelectricsheets are stacked and sintered. The dummy electrodes 73 a, 73 b, 73 care grounded through a ground electrode. As is the case with thepiezoelectric actuator 3A described above, if the shrinking percentageduring sintering of the dummy positive electrodes is within a certainrange where the restraining layer 70 is prevented from warping, thisrestraining layer 70 could include only the piezoelectric sheets thatare identical in structure to the piezoelectric sheets 40 a, 40 b, 40 c,71 b.

[0088] The operation of the piezoelectric actuator 3 will be describedbelow with reference to FIGS. 2 and 3.

[0089] When the controller causes the switch 62 a, for example, to beclosed in accordance with certain print data, voltage is applied betweenthe internal negative electrodes 42 and the internal positive electrodes44 a, generating electric fields in the piezo-electrically activeportions 46 a of the piezoelectric sheets 40 a to 40 f. Consequently,the electrostrictive effects of the piezoelectric sheets develop forcewith which the active portions 46 a tend to vertically expand, in FIG.2. In the meantime, because no electric field is generated in thepiezoelectric sheets 71 a, 71 b, 71 c of the restraining layer 70, thesesheets 71 a, 71 b, 71 c do not expand nor contract. Therefore, the forcewith which the active portions 46 a tend to vertically expand deformsthe active layer 38 mainly downward. As indicated with an arrow in FIG.3, the downward deformed active layer 38 reduces the volume of the inkchannel 32 a. This ejects an ink droplet 39 from the ink channel 32 athrough the orifice 37 a. When the switch 62 a is opened to cut off thevoltage application, the piezo-electrically active portions 46 a returnto their original conditions. This enlarges the ink channel 32 a,thereby supplying it with ink from the supply device 16 (FIG. 1) througha valve (not shown).

[0090] Without the restraining layer 70, the deformation of thepiezo-electrically active portions 46 a would deform the active layer 38equally upward and downward. When the restraining layer 70 is providedas the piezoelectric actuator 3 of the embodiment, the restraining layer70, which is highly rigid, and the active layer 38 are sintered into onepiece. Even when the switch 62 a is closed, no electric field isgenerated in the restraining layer 70, which does therefore not deform.Consequently, the deformation caused in the active layer 38 mainlydeforms the lower side of this layer 38, which is adjacent to the inkchannel 32 a. Accordingly, the lower side of the piezoelectric actuator3 can be deformed larger than that of a piezoelectric actuator without arestraining layer 70, if the piezo-electrically active portions of theseactuator deform equally in amount. This makes it possible to reduce thecapacity of the ink channel 32 a and eject a larger amount of ink. Thatis to say, even with the same voltage applied, the provision of therestraining layer 70 makes it possible to eject a larger amount of ink.In other words, it is possible to eject a certain amount of ink byapplying a lower voltage. This results in smaller electric power.

[0091] In the embodiment, as described above, the thickness of thepiezoelectric sheets 40, 71, on which the electrodes and the like areprinted, is between 5-40 μm. Thus, excellent piezoelectriccharacteristics can be obtained and the active layer 38 can sufficientlydeform. Relationship between the thickness of the piezoelectric sheetand the piezoelectric characteristics and between the thickness of thepiezoelectric sheet and the deformation of the active layer will bedescribed with reference to FIG. 4.

[0092] As shown in FIG. 4, when the thickness of the piezoelectric sheetis 15 μm or more, the piezoelectric constant d33 is about 600(×10⁻¹²m/V). Therefore, the excellent characteristics can be obtained.

[0093] However, when it is less than 5 μm, the piezoelectric constantd33 is less than 450(×10⁻¹² m/V), so that the sufficient characteristicscannot be obtained.

[0094] This is because when the thickness of the piezoelectric sheet isless than 5 μm, the silver (Ag) in the electrodes diffuses too muchduring sintering. Accordingly, piezoelectric sufficient characteristicscannot be obtained as described above.

[0095] Therefore, in the embodiment, the thickness of the onepiezoelectric sheet is 5 μm or more, preferably, 15 μm or more. Thus,sufficient piezoelectric characteristics can be obtained in the activelayer 38.

[0096] As shown in FIG. 4, when thickness of the piezoelectric sheet is30 μm or less, the amount of deformation of the active layer 38 is 20 nmor more. The amount of deformation shown in FIG. 4 is that which occurswhen the voltage of 20 V is applied to five piezoelectric sheets of theactive layer 38.

[0097] As can be seen from FIG. 4, when piezoelectric sheet thicknessexceeds 40 μm, the amount of deformation of the active layer 38 is 13 μmor less. Therefore, sufficient deformation cannot be obtained.

[0098] This is because when the thickness of the piezoelectric sheetexceeds 40 μm, the restraint of the non-active portions have a greateffect on the active portions. Accordingly, the active portions cannotsufficiently deform.

[0099] Thus, in the embodiment, the thickness of the piezoelectric sheetis 40 μm or less, preferably 30 μm or less. As a result, a sufficientamount of deformation can be obtained in the active layer 38.

[0100] In the embodiment, as described above, the internal negativeelectrode 42 and the internal positive electrodes 44 a, 44 b, 44 c eachhave the thickness of about between 0.7-5 μm, preferably between 1-3 μm.Therefore, the electrodes do not become too narrow and are not cut off.Delamination hardly occurs at the interface between the portions havingthe internal electrodes and the portions not having the internalelectrodes. Relationships between a thickness of an internal electrodeand a capacitance will be described with reference to FIG. 5.

[0101] As shown in FIG. 5, when the thickness of an internal electrodeis 1 μm or more, the capacitance of 1600 pF can be obtained. Therefore,an electrode having a sufficient width can be formed.

[0102] However, when the thickness of the internal electrode is lessthan 0.7 μm, the capacitance is less than 1500 pF, and the electrodebecomes narrow. Further, when it is less than 0.5 μm, the capacitance isless than 500 pF, thereby causing the electrode to be cut off.

[0103] This occurs because when the thickness of the internal electrodeis less than 0.7 μm, the silver (Ag) in the electrodes diffuses duringsintering. Accordingly, the electrode becomes too narrow or is cut off.

[0104] Thus, in the embodiment, the thickness of the internal electrodefilm is 0.7 μm or more, preferably 1 μm or more. As a result, theinternal negative electrode 42 and the internal positive electrodes 44a, 44 b, 44 c having sufficient width can be formed.

[0105] As shown in FIG. 5, when the internal electrode thickness exceeds5 μm, delamination frequently occurs at the interface between theportions having the internal electrodes and the portions not having theinternal electrodes.

[0106] This is because when the thickness of the internal electrode filmexceeds 5 μm, the difference of the thickness between the portionshaving the internal electrodes and the portions not having the internalelectrodes, in the piezoelectric sheet, is too great.

[0107] Accordingly, in the embodiment, the thickness of the internalelectrode is 5 μm or less, preferably 3 μm or less. As a result, theelectrodes having sufficient width can be obtained and delamination atthe interface between the laminated piezoelectric sheets can beprevented.

[0108] As described above, in the embodiment, the thickness of the onepiezoelectric sheet is between 5-40 μm, preferably between 15-30 μm,thereby excellent piezoelectric characteristics and a desired amount ofdeformation can be obtained in the active layer 38. Accordingly,ejection characteristics of each ink chamber becomes stable and theejection characteristics can be prevented from variation.

[0109] As described above, the thickness of the internal electrode isbetween 0.7-5 μm, preferably between 1-3 μm. Thus, physical defectstraceable to the electrodes can be prevented, so that originalpiezoelectric characteristics can be obtained.

[0110] In the exemplary embodiments described above, a piezoelectricelement that actuates in an extension mode has been described. However,the scope of the invention is not restricted to such as that describedabove. The same concepts can be applied to a piezoelectric element withany mode, such as an unimorph mode, a bimorph mode, and a share mode.Further, in the embodiments described above, as shown in FIGS. 2, 3, 8and 9, the bottom sheet of the piezoelectric actuator 15 has theinternal positive electrode 44 a. However, the internal negativeelectrode 42 can be provided onto the bottom sheet by changing the orderof the laminated layers. As shown in FIGS. 8 and 9, in order to improvethe stiffness of the actuator and the efficiency of deformation of eachchannel, the piezoelectric actuator 15 is provided with the restraininglayer 70A or 70B. In the embodiments described thus far, the restraininglayer 70A, 70B also has the electrodes, however, these electrodes can beomitted to make a layer which does not have any electrode.

[0111] Another embodiment of the invention will be described withreference to FIGS. 10 to 20.

[0112] As shown in FIG. 10, an ink jet print head 101 includes a cavityplate 110 formed by stacking substantially rectangular metal plates, inwhich a plurality of pressure chambers 116, which extend in a directionperpendicular to a longitudinal direction of the cavity plate 110, areformed so as to be aligned in parallel with the longitudinal directionof the cavity plate 110. A plate-like piezoelectric actuator 120 havinga substantially rectangular plate shape is bonded to the cavity plate110 so as to close the pressure chambers 116. A flat flexible cable 150for connecting with external equipment is bonded on the piezoelectricactuator 120.

[0113] As shown in FIGS. 10 and 11, surface electrodes 131, 132 areprovided on piezoelectric actuator 120 at its surface opposite to thesurface to be bonded to the cavity plate 110 (an upper surface of theplate-like piezoelectric actuator 120 in FIG. 10). The surfaceelectrodes 131 and 132 connect with driving electrodes 136 describedlater and common electrodes 135 described later, respectively. Inaddition, pseudo electrodes 140 described later are aligned in two rowson the surface of the piezoelectric actuator 120.

[0114] Referring to FIGS. 12 to 14, a structure of the ink jet headstructured described above will be described.

[0115] As shown in FIGS. 12 to 14, the piezoelectric actuator 120 isconstructed by stacking ten piezoelectric sheets 121, 122, 123, 124,125, 126, 127, 128, 129, 130 in this order from above. The piezoelectricsheets 126, 128, 130 are identical in structure. On the upper surface ofeach piezoelectric sheet 126, 128, 130, the elongate driving electrodes136 are formed on positions corresponding to the respective pressurechambers 116 formed in the cavity plate 110. As shown in FIG. 13,connectors 136 a are formed at sides 126 a, 126 b of the piezoelectricsheet 126. Quasi pattern electrodes 136′, which is a land pattern thatdoes not contribute to deformation of the piezoelectric sheets, areformed on positions corresponding connectors 135 a of the commonelectrodes 135, on the upper surface of the piezoelectric sheets 126,128, 130.

[0116] As shown in FIGS. 13 and 14, the piezoelectric sheets 123, 124,125, 127, 129 are identical in structure. On the upper surface of eachpiezoelectric sheet 123, 124, 125, 127, 129, is the band-shape commonelectrode 135, which is a common electrode for all of the pressurechambers 116. The connectors 135 a of each common electrode 135 areformed at the sides 123 a, 123 b of the piezoelectric sheets 123, 124,125, 127, 129. Quasi pattern electrodes 135′, which is a land patternthat does not contribute to deformation of the piezoelectric sheets, areformed on positions corresponding to the connectors 136 a of the drivingelectrodes 136, on the upper surface of the piezoelectric sheets 123,124, 125, 127, 129. The thickness of the quasi pattern electrodes 135′,136′ is the same as that of the driving electrodes 136 and the commonelectrodes 135, so that recessed portions in the piezoelectric sheetswhere the driving electrodes 136 and the common electrodes 135 do notexist will be flattened when the piezoelectric sheets are laminated.

[0117] As shown in FIG. 13, on the upper surface of the piezoelectricsheet 121, the surface electrodes 131 and 132, which correspond to therespective driving electrodes 136 and the common electrode 135,respectively, are provided along long sides 121 a, 121 b of thepiezoelectric sheet 121. The surface electrodes 131 and 132 are providedwith respect to the upper surface of the cavity plate 110 between theline of the pressure chambers 116 and slots 141 and 142. Between thesurface electrodes 131 aligned along the side 121 a of the piezoelectricsheet 121 and the surface electrodes 131 aligned along the side 121 b ofthe piezoelectric sheet 121, the substantially rectangular pseudoelectrodes 140 are provided with respect to lands 116 e (see FIG. 12),which are provided to the cavity plate 110 to separate the adjacentpressure chambers 116. The thickness of the pseudo electrodes 140 isabout the same as that of the surface electrodes 131.

[0118] The pseudo electrodes 140 are not connected with the commonelectrodes 135 nor the driving electrodes 136. When the piezoelectricactuator 120 is bonded to the cavity plate 110, the pseudo electrodes140 contacts an assembly jig 160. While the piezoelectric sheet 122 ismade of the same material as the piezoelectric sheet 121, no electrodeis provided to the piezoelectric sheet 122.

[0119] As shown in FIG. 12, after the piezoelectric sheets 121 to 130are stacked as described above, external electrodes 133 and 134 areformed on the right and left sides so as to be perpendicular to theupper and lower surfaces of the piezoelectric sheets 121 to 130. Theexternal electrodes 133 electrically connect the driving electrodes 136with the respective surface electrodes 131. The external electrodes 134electrically connect the common electrodes 135 with the respectivesurface electrodes 132.

[0120] In the piezoelectric actuator 120 of the embodiment, the drivingelectrodes 136 are provided on the three piezoelectric sheets 126, 128,130. However, the driving electrodes 136 may be provided on any numberof sheets, for example, one, two or five of the piezoelectric sheets 121to 130. In accordance with the number of piezoelectric sheets on whichthe driving electrodes 136 are provided, a corresponding number ofpiezoelectric sheets each of which has a common electrode 135 may beprovided.

[0121] Next, a producing method of the piezoelectric sheets 121 to 130will be described. The piezoelectric sheets 121 to 130 are produced bythe following method. First, ceramic powder of ferroelectric leadzirconate titanate (PZT (PbTiO₃·PbZrO₃)) material, a binder and asolvent are mixed into a mixed liquid having a viscosity between 10,000and 30,000 CPS. The mixed liquid is spread and dried on films ofpolyethylene terephthalate (PET) or other plastic material to form tenpiezoelectric sheets. Each of the piezoelectric sheets has thickness ofbetween 5-40 μm, preferably between 15-30 μm. In this exemplaryembodiment, the thickness of each of the piezoelectric sheets is madebetween about 22.5-30 μm. Metallic material is screen-printed onportions of three of the piezoelectric sheets to make the drivingelectrodes 136 and the quasi pattern electrodes 136′. These three sheetswill be the piezoelectric sheets 126, 128, 130.

[0122] As is the case with the first embodiment, the width of thedriving electrodes is between 50-500 μm, preferably between 80-200 μm,and the thickness of them is between 0.7-5 μm, preferably between 1-3μm.

[0123] Metallic material is screen-printed on portions of the other fiveof the piezoelectric sheets which portions will be the common electrodes135 and the quasi pattern electrodes 135′. These five piezoelectricsheets will be the piezoelectric sheets 123, 124, 125, 127, 129.Likewise, metallic material is screen-printed on portions of anotherother one of the piezoelectric sheets to make the surface electrodes131, 132 and the pseudo electrodes 140. This piezoelectric sheet will bethe piezoelectric sheet 121. The last one of the piezoelectric sheets isnot printed with any electrodes. This sheet will be the piezoelectricsheet 122.

[0124] The ten piezoelectric sheets 130, 129, 128, 127, 126, 125, 124,123, 122, 121 are alternatively stacked, in this order, from belowupward, with the piezoelectric sheet 130 positioned at the bottom. Thestacked piezoelectric sheets 130 to 121 are pressed with heat, degreasedand sintered to form a piezoelectric block. Then, the externalelectrodes 133, 134 are formed at the sides of the piezoelectric block.The laminated block thus constructed is then immersed in an oil bath(not shown) filled with a silicone oil or another insulating oil at atemperature of about 130° C. All of the surface electrodes 131 areconnected to a positive voltage power supply and all of the surfaceelectrodes 132 are connected to the ground. An electric field of about2.5 kv/mm is applied between surface electrodes 131 and 132 to polarizethe portions between the driving electrodes 136 and the commonelectrodes 135 of the piezoelectric sheets 125 to 129. Thus, theplate-like piezoelectric actuator 120 is obtained.

[0125] The surface electrodes 132 are connected to the ground and thedriving voltage is applied to either one of the surface electrodes 131.An electric field is generated in parallel to the polarized direction atthe piezoelectric sheets 125 to 129 between the common electrodes 135and the driving electrodes 136 which are connected to the surfaceelectrode 131 to which the driving voltage is applied. The piezoelectricsheets 125 to 129 expand to apply pressure to ink in the pressurechambers 116 of the cavity plate 110. Thus the piezoelectric sheets 125to 129 between the common electrodes 135 and the driving electrodes 136act as the active layers. There is a difference in shrinking percentagebetween the piezoelectric ceramic and the metallic material constitutingthe electrodes when the piezoelectric sheets 121 to 130 are sintered.Therefore, the piezoelectric sheets 121 to 124 function as a restraininglayer in order to prevent warps and/or waves to keep the flatness in thepiezoelectric sheets 121 to 130 of the active layer after sintering ofthe piezoelectric sheets 121 to 124 and in order to make the activelayer of the piezoelectric sheets 125 to 129 deform only toward thepressure chambers 116.

[0126] The cavity plate 110 will be described with reference to FIGS. 15and 16.

[0127] As shown in FIGS. 15 and 16, the cavity plate 110 has five metalplates, namely, a nozzle plate 111, two manifold plates 112, 112, aspacer plate 113, and a base plate 114. These five plates are stacked inthis order from below upward.

[0128] As shown in FIGS. 15 and 16, in the nozzle plate 111, a pluralityof nozzles 115 having an extremely small diameter, are provided with asmall pitch P, along a center line 111 a parallel to the longitudinaldirection of the nozzle plate 115. In the two manifold plates 112, 112,a plurality of through holes 117 are provided to be aligned with thenozzles 115, and ink passage 112 a are provided along both sides of therow of the through holes 117. The ink passages 112 a, 112 a are closedby the spacer plate 113 contiguous to the upper manifold plate 112.

[0129] In the base plate 114, a plurality of narrow pressure chambers116 are provided so as to laterally extend to the center line 114 a andthe row of the pressure chambers 116 are arranged parallel to thelongitudinal direction. Each pressure chamber 116 includes an ink outlet116 a and an ink inlet 116 b. The ink outlet 116 a is positioned on thecenter line 114 a. The pressure chambers 116 alternatively extends inthe opposite directions with their ink outlets 116 a aligned on thecenter line 114 a. The ink inlets 116 a communicate with the nozzles 115in the base plate 111, via the through holes 117 having the extremelysmall diameter and formed in the spacer plate 113 and the manifoldplates 112, 112. The ink inlets 116 b of the pressure chambers 116communicate with the ink passages 112 a in the manifold plates 112, viathrough holes 118 formed in the spacer plate 113.

[0130] Ink flows into the ink passages 112 a from ink supply holes 119a, 119 b formed in one end portion of the spacer plate 113 and the baseplate 114, and then is distributed to the pressure chambers 116 via thethrough holes 118. After that, the ink is supplied to the respectivenozzles 115 corresponding to the pressure chambers 116 via the throughholes 117.

[0131] Each pressure chamber 116 is provided with an orifice 116 c at aposition adjacent to the ink inlet 116 b. The orifice 116 c is a shallowrecess and regulates an amount of ink flow. Each pressure chamber 116 isstrengthened by a beam 116 d, which is integrally provided at asubstantially middle of each pressure chamber 116. As shown in FIG. 16,between the pressure chambers 116 in the base plate 114, a land 116 e isprovided to separate the adjacent pressure chambers 116.

[0132] The piezoelectric actuator 120 constructed as described above isbonded to the cavity plate 110 so that the lower surface of thepiezoelectric plate 130 of the piezoelectric actuator 120 closes thepressure chambers 116 of the cavity plate 110. On the upper surface ofthe piezoelectric plate 121 of the piezoelectric actuator 120, theflexible flat cable 150 is stacked and pressed, thereby wiring patterns(not shown) in the flexible flat cable 150 are electrically connectedwith the surface electrodes 131, 132. Slots 141 and 142 are provided onthe top surface of the base plate 114 with respect to the bottom ends ofthe external electrodes 133 and 134 so that the external electrodes 133and 134 do not electrically contact with the base plate 114.

[0133] Next, a process of adhering the piezoelectric actuator 120 to thecavity plate 110 will be described with reference to FIGS. 17 to 20.

[0134] First, as shown in FIG. 17, the cavity plate 110 is placed on aworkbench 170 having a flat surface. Next, as shown in FIG. 18, thepiezoelectric actuator 120, to which an adhesive is applied at itsbottom, is placed on the cavity plate 110 on the workbench 170, whilechecking to make sure that the cavity plate 110 is in proper alignmentwith the piezoelectric actuator 120. Then, as shown in FIG. 19, a forceof 10 kg-weight is applied to the upper surface of the piezoelectricactuator 120, in a direction indicated with an arrow B, using anassembly jig 160 having a flat bottom surface. Thus, the piezoelectricactuator 120 is bonded to the cavity plate 110.

[0135] The surface electrodes 131, 132 provided on the piezoelectricactuator 120 correspond to the outer side portions of the line of thepressure chambers 116 of the upper surface of the cavity plate 110 andthe pseudo electrodes 140 correspond to the lands 116 e between thepressure chambers 116. At that time, the pressing force from theassembly jig 160 is applied so as to press the piezoelectric actuator120 to the upper surface of the cavity plate 110. Therefore, even ifthere are waves in the piezoelectric actuator 120, the waves can beflattened by the force transmitted from the assembly jig 160 via thepseudo electrodes 140 formed in the middle of the piezoelectric actuator120. Accordingly, the piezoelectric actuator 120 can be surely bonded tothe cavity plate 110 without clearances or voids.

[0136] As shown in FIG. 20, with the adhesion method described above,the piezoelectric actuator 120 can be surely bonded to the cavity plate110 without clearances or voids. Accordingly, the piezoelectric actuator120 is intimately bonded to the cavity plate 110, so that the adhesionof the piezoelectric actuator 120 and the cavity plate 110 is improvedand the ink leakage from the pressure chambers 116 can be minimized orprevented. Thus, the development of defects in the ink jet print heads101 can also be minimized or prevented.

[0137] The shape of the pseudo electrode 140 is not restricted to thestrip shape. For example, the pseudo electrode 140 can have a wideband-shape projection like the common electrode 135. While the surfaceelectrodes 131 and 132 are connected to the driving electrodes 136 andthe common electrodes 135, respectively, by externally providing theelectrodes 133 and 134, they may be connected to each other by providingelectrodes in through holes formed in piezoelectric sheets. The pressurechambers 116 can be arranged in more than three lines by providing thedriving electrodes 136 in the respective multiple lines.

[0138] Another exemplary embodiment of the invention will be describedwith reference to FIGS. 21 to 31B.

[0139] As shown in FIG. 23, a frame 201 to be mounted on a carriage isformed into substantially a box with its upper surface open. A mount 203is formed in the frame 201, and four ink cartridges (not shown) forsupplying ink are detachably mounted to the mount 203 from above theframe 201. On one side 203 a of the mount 203, ink supply passages 204a, 204 b, 204 c, 204 d connected to ink discharge ports (not shown) areformed so as to pass through a bottom plate 205 of the frame 201. Arubber packing (not shown) is disposed on the upper surface of the oneside 203 a of the mount 203 so as to intimately contact the inkdischarge ports (not shown) of the ink cartridges.

[0140] The bottom plate 205 is stepped down from the mount 203 so as tohorizontally project there from. As shown in FIGS. 22 and 24, on theunderside of the bottom plate 205, two stepped supports 208, 208 areformed to receive two front head units 206, side by side, as describedlater. In the bottom plate 205, a plurality of recesses 209 a, 209 b,which are filled with an UV adhesive to bond the front head units 206,are formed so as to penetrate the bottom plate 205.

[0141] As shown in FIGS. 25 and 26, the front head unit 206 isconstructed from a cavity plate 210 constructed by laminating aplurality of thin metal plates, a plate-like piezoelectric actuator 220laminated to the cavity plate 210 using an adhesive or an adhesivesheet, and a flexible flat cable 240 bonded, using an adhesive, to theupper surface of the piezoelectric actuator 220 for electric connectionwith external equipment. Nozzles 215 are formed on the underside of thecavity plate 210 at the bottom and ink is ejected downward there from.

[0142] The cavity plate 210 is constructed as shown in FIG. 28. Fivethin metal plates, namely, a nozzle plate 211, two manifold plates 212,a spacer plate 213, and a base plate 214, are laminated in this orderusing an adhesive. In this embodiment, each of plates 211 to 214 is asteel plate alloyed with 42% nickel, about 50-150 μm thick. These plates211 to 214 may be formed of for example, resins, instead of metals.

[0143] In the nozzle plate 211, a plurality of nozzles 215 having anextremely small diameter (the order of 25 μm in diameter in thisembodiment) are provided with a small pitch P, in a staggeredconfiguration, along center lines 211 a, 211 b extending in alongitudinal direction of the nozzle plate 211. The manifold plates 212,212 are sandwiched between the nozzle plate 211 and the spacer plate 213so as to be closed by them.

[0144] As shown in FIG. 28, in the base plate 214, a plurality of narrowpressure chambers 216 are provided, in a staggered configuration, so asto extend in a direction perpendicular to the center lines 214 a, 214 bin the longitudinal direction. Each pressure chamber 216 has an inkoutlet 216 a, an ink inlet 216 b and an orifice 216 d. The ink inlets216 b communicate with common pressure chambers 212 a in the manifoldplates 212, via the ink supply holes 218 provided on right and left sideportions of the spacer plate 213. A cross-sectional area of the orifice216 d perpendicular to an ink flow direction is smaller than that of thepressure chamber 216. By doing so, the resistance to the flow of ink canbe increased.

[0145] The ink outlet 216 a of each pressure chamber 216 is positionedso as to be aligned with an associated one of the nozzles 215 in thenozzle plate 211. The ink inlets 216 a communicate with the spacer plate213 and the manifold plates 212, 212, via the through holes 217 havingan extremely small diameter and are formed in the staggeredconfiguration similarly to the nozzles 215.

[0146] As shown in FIG. 29, the piezoelectric actuator 220 isconstructed by laminating three piezoelectric sheets 221, 222, 223. Onthe upper surface of the lowermost piezoelectric sheet 221, a pluralityof narrow driving electrodes 224 are provided in a staggeredconfiguration so as to be aligned with the respective pressure chambers216 in the cavity plate 210. A connector 224 a of each driving electrode224 is provided at a side 220 c perpendicular to an upper side 220 a andan underside 220 b of the piezoelectric actuator 220.

[0147] On the upper surface of the piezoelectric sheet 222, a commonelectrode 225 is formed so as to be aligned with the pressure chambers216. As is the case with the driving electrodes 224, connectors 225 a ofthe common electrode 225 are provided at the right and left sides 220 c.

[0148] On the upper surface of the topmost piezoelectric sheet 223,surface electrodes 226 aligned with the respective driving electrodes224 and surface electrodes 227 aligned with the common electrode 225 areprovided along the right and left sides 220 c.

[0149] As is the case with the first embodiment, the width of thedriving electrodes is between 50-500 μm, preferably between 80-200 μm,and the thickness of them is between 0.7-5 μm, preferably between 1-3μm.

[0150] At the right and left sides 220 c, first and second grooves 230,231 are formed in the laminating direction. The first grooves 230 areprovided to the portions where the connectors 224 a of the drivingelectrodes 224, the surface electrodes 226 and quasi pattern electrodes229 exist. The second grooves 231 are provided to the portions where theconnectors 225 a of the common electrodes 225, the surface electrodes227 and quasi pattern electrodes 228 exist. As shown in FIG. 26, anexternal electrode 232 is provided in each first groove 230 toelectrically connect the driving electrodes 224 with the respectivesurface electrodes 226. An external electrode 233 is provided in eachsecond groove 231 electrically connect the common electrode 225 with thesurface electrodes 227.

[0151] Each area in the piezoelectric sheet 222 sandwiched between thecommon electrode 225 and the driving electrodes 224 is polarized to beprovided with the piezoelectric characteristics. As a result, theseareas become piezo-electrically active portions corresponding to therespective pressure chambers 216.

[0152] The cavity plate 210 and the piezoelectric actuator 220constructed as described above are laminated each other so that thepressure chambers 216 of the cavity plate 210 are aligned with therespective driving electrodes 224 of the piezoelectric actuator 220. Theflexible flat cable 240 is provided and pressed over the upper surface220 a of the piezoelectric actuator 220. As a result, a wiring pattern(not shown) of the flexible flat cable 240 is electrically connectedwith the surface electrodes 226, 227.

[0153] In such a construction, voltage is applied between the arbitrarydriving electrodes 224 and the common electrode 225 of the piezoelectricactuator 220, generating electric fields in the driving electrodes 224applied with the voltage, that is, in the piezo-electrically activeportions of the piezoelectric sheets 222. Consequently, theelectrostrictive effects of the piezoelectric sheets develop deformationin the piezo-electrically active portions in the laminating direction.The internal volume of the pressure chambers 216 corresponding to thedriving electrodes 224 are reduced by the pressure produced due to thedeformation. As a result, ink in the pressure chambers 216 is ejectedfrom the nozzles 215, and thus printing is performed.

[0154] A fabricating method of the piezoelectric actuator 220 will bedescribed. First, ceramic powder of ferroelectric lead zirconatetitanate (PZT (PbTiO₃·PbZrO₃)) material, a binder and a solvent aremixed into a mixed liquid.

[0155] Next, the mixed liquid is applied on plastic films to be apredetermined thickness, using the doctor blade method, to form threepiezoelectric sheets 221, 222, 223.

[0156] Each of the piezoelectric sheets has a thickness of between 5-40μm, preferably between 15-30 μm.

[0157] Metallic material is screen-printed on those portions of thepiezoelectric sheets 221, 222, 223 which will be electrodes, such as thedriving electrodes 224.

[0158] Then, the piezoelectric sheets 221, 222, 223 formed as describedabove are stacked and pressed with heat to form a laminated block.

[0159] Next, the binder in the laminated block is burned by applyingheat at a predetermined temperature. After that, the laminated block issintered in a calcining furnace at a predetermined temperature.

[0160] Then, the laminated block is cut into smaller blocks having apredetermined size, thereby obtaining several piezoelectric actuators220.

[0161] Then, the external electrodes 232, 233 are printed on theindividual piezoelectric actuators 220 in the calcining furnace.

[0162] Next, a high voltage is applied between the electrodes 224 and225 to polarize the piezoelectric sheet 221.

[0163] As described above, the piezoelectric actuators 220 to be used inthe piezoelectric ink jet head of the embodiment are fabricated.

[0164] According to the fabricating method described above, thepiezoelectric actuator 220, having extremely narrow electrodes of awidth of 250 μm or smaller, or a width of 200 μm, can be obtained.

[0165] In particular, in this embodiment, the surfaces of thepiezoelectric actuator 220 and the cavity plate 210 to be adhered toeach other have a flatness such that the difference in height ofasperities on the surfaces are 30 μm or less in an area of 5 mm².

[0166] Therefore, when the piezoelectric actuator 220 of this embodimentis bonded to the cavity plate 210, grinding of the surfaces, which isconventionally performed, can be omitted. In addition, the piezoelectricactuator 220, with the as-is state of a sintered body, can be bonded tothe cavity plate 210 with no further process. Accordingly, the operatingefficiency in the process of fabricating the piezoelectric actuator 220can be improved and the fabricating cost can be reduced.

[0167] In this embodiment, the flatness of the surface of the plasticfilm forming the piezoelectric sheets, the pressing surface of theheat-pressing device, and the surface of the workbench on which thelaminated block is to be placed when the binder eliminating process andthe sintering process are implemented, have the flatness such that thedifference in height of asperities on the surfaces is 30 μm or less inthe area of 5 mm². Specifically, foreign substances are removed fromthese surfaces before materials are placed thereon.

[0168] As a result of removing foreign substances at each process, thelaminated block is sintered with no foreign substances, so thatasperities are hardly developed on the laminated block.

[0169] In particular, the height of projections formed on the surfacesto be bonded is 10 μm or less and the depth of the depressions is 20 μmor less. Therefore, the difference of the height between the projectionsand the depressions is 30 μm in the area of 5 mm².

[0170] Referring to FIGS. 30A, 30B, 31A and 31B, profiled data of thesurface of the piezoelectric actuators 220 before external electrodesare printed thereon, will be described. These piezoelectric actuators220 are obtained by cutting the laminated block sintered according tothe process described above.

[0171]FIG. 30A is a three-dimensional view showing a surface of onesample of the piezoelectric actuator 220, wherein the surface is dividedinto 208 (8×26) sections. The piezoelectric actuator 220 is divided into8 sections in a lateral direction and 26 sections in a longitudinaldirection. The pressure chambers 216 and the nozzles 215 are alignedalong the longitudinal direction.

[0172] In the cavity plate 210, 75 sets of the pressure chambers 216 andthe nozzles 215 are arrayed in a row and another 75 sets of pressurechambers 216 and the nozzles 215, which are bilaterally symmetrical withthose shown in FIG. 27, are arrayed in a row. A total of 150 sets ofpressure chambers 216 and nozzles 215 are therefore arrayed in two rowssuch that 150 nozzles are aligned in a row.

[0173] A number is serially assigned to the 75 sets of the pressurechambers 216 and the nozzles 215 aligned in the two rows as describedabove. Even numbers are assigned to one row of the 75 sets of thepressure chambers 216 and the nozzles 215, and odd numbers are assignedto another row of the 75 sets of the pressure chambers 216 and thenozzles 215. FIG. 30A is a three-dimensional surface profiling dataviewed from a #1 side and the even number row side (EVEN side). Ahypothetical plane is calculated based on the heights of the corners ofthe piezoelectric actuator 220. Then heights of each section from thehypothetical plane is calculated. In FIG. 30A, the areas A, B, C showthat the height is between 0.02-0.03 mm, 0.01-0.02 mm, and 0-0.01 mm,respectively.

[0174]FIG. 30B corresponds to a diagram rotated 180 degrees from thatshown in FIG. 30A and shows a three-dimensional surface profiling dataviewed from a #150 side and the odd number row side (ODD side). Theareas A, B, C show that the height is between 0.02-0.03 mm, 0.01-0.02mm, and 0-0.01 mm, respectively.

[0175]FIG. 31A is a line graph showing inclination of the surface in thelateral direction, by eight sections, in FIG. 30A. The line graph showsinclination of the surface in the lateral direction, by eight sections,at a position #1-#2 corresponding to the pressure chambers and nozzles#1-#2 positioned in a nearest side, a position #75-#76 corresponding tothe pressure chambers and nozzles #75-#76 positioned in a middle in thelongitudinal direction and a position #149-#150 corresponding to thepressure chambers and nozzles #149-#150 positioned in a farthest side.FIG. 31B is a line graph showing inclination of the surface in thelongitudinal direction, by 26 sections, in FIG. 30A, at a position#2-150 corresponding to the pressure chambers and nozzles #2-#150, amiddle, and at a position #1-#149 corresponding to the pressure chambersand nozzles #2-#150. These data are measured by NEXIV.

[0176] As seen from FIG. 31B, a vicinity of a section #21 showing themiddle of the surface is depressed as compared with that of thepositions #2-#150 and #1-#149. However, the difference of the height ofthe section #21 between the middle and the positions #2-#150 and #1-#149is 10 μm or less.

[0177] Thus, as seen from FIGS. 30A, 30B, 31A and 31B, in thepiezoelectric actuators 220 fabricated according to the method of thisembodiment, the height of the projections of their surfaces is 10 μm orless and the depth of the depressions is 10 μm or less in the area of 5mm². Therefore, the difference of the height between the projection andthe depression is 20 μm or less.

[0178] Accordingly, the piezoelectric actuator 220 with the as-is stateof a sintered body can be bonded to the cavity plate 210 withoutgrinding the surface of the piezoelectric actuator 220. Consequently,the operating efficiency in the process of fabricating the piezoelectricactuator 220 can be improved and the fabricating cost can be alsoreduced.

[0179] As is the case with the second embodiment, pseudo electrodeshaving the same thickness as the surface electrodes 226, 227 can beprovided between the surface electrodes 226 and 227 provided on theupper surface of the topmost piezoelectric sheet 223.

[0180] While the invention has been described in detail with referenceto specific embodiments thereof, it would be apparent to those skilledin the art that various changes and modifications may be made thereinwithout departing from the spirit of the invention.

What is claimed is:
 1. An ink jet print head, comprising: a cavity platethat includes a plurality of nozzles and a plurality of pressurechambers communicating with the respective nozzles; and a plate-likepiezoelectric actuator formed into a single laminated structure bylaminating a plurality of piezoelectric sheets including a plurality ofelectrodes which are formed at positions so as to be aligned with therespective pressure chambers, the laminated piezoelectric actuatorsintered and bonded to the cavity plate so as to close the pressurechambers provided in the cavity plate, wherein each of the piezoelectricsheets has a thickness of between 5-40 μm.
 2. The ink jet print headaccording to claim 1, wherein each of the piezoelectric sheets has athickness of between 15-30 μm.
 3. The ink jet print head according toclaim 2, wherein the electrodes are driving electrodes, which are formedat positions with respect to the pressure chambers, and commonelectrodes, which are formed at a position to cover the pressurechambers, wherein each of the driving electrodes has a width of between50-500 μm and a thickness of between 0.7-5 μm.
 4. The ink jet print headaccording to claim 3, wherein each of the driving electrodes has a widthof between 80-200 μm and a thickness of between 1-3 μm.
 5. The ink jetprint head according to claim 2, wherein the piezoelectric actuator hasa flatness of 30 μm or less, which is a difference of height betweenprojections and depressions formed on the piezoelectric actuator at itssurface to which the cavity plate is bonded.
 6. The ink jet print headaccording to claim 5, wherein the piezoelectric actuator has theflatness of 30 μm or less in an area of 5 mm².
 7. An ink jet print head,comprising: a cavity plate that includes a plurality of nozzles and aplurality of pressure chambers communicating with the respectivenozzles; a plate-like piezoelectric actuator formed into a singlelaminated structure by laminating a plurality of piezoelectric sheetsincluding a plurality of electrodes which are formed at positions so asto be aligned with the respective pressure chambers, the laminatedpiezoelectric actuator sintered and bonded to the cavity plate so as toclose the pressure chambers provided in the cavity plate; surfaceelectrodes provided at an end portion of a surface of the piezoelectricactuator, which is opposed to a surface to be bonded to the cavityplate, and electrically connected with the plurality of electrodes; andprotrusions that each has a thickness of the surface electrodes and isprovided on the surface of the piezoelectric actuator where the surfaceelectrodes are provided.
 8. The ink jet print head according to claim 7,wherein the plurality of pressure chambers are aligned in a number ofrows, the surface electrodes connected with the electrodes are alignedin a number of rows at both end portions along the rows of the pressurechambers, and the protrusions are disposed between the rows of thesurface electrodes.
 9. The ink jet print head according to claim 8,wherein the cavity plate has beams to separate the adjacent pressurechambers, and the protrusions are provided on the surface of thepiezoelectric actuator with respect to the beams.
 10. The ink jet printhead according to claim 9, wherein the surface electrodes and theprotrusions are printed on the surface of the piezoelectric actuatorusing the same material.
 11. The ink jet print head according to claim10, wherein each of the piezoelectric sheets has a thickness of between15-30 μm.
 12. The ink jet print head according to claim 10, wherein eachof the piezoelectric sheets has a thickness of between 22.5-30 μm. 13.The ink jet print head according to claim 11, wherein the electrodes aredriving electrodes, which are formed at positions with respect to thepressure chambers, and common electrodes, which are formed at a positionto cover the pressure chambers, wherein each of the driving electrodeshas a width of between 50-500 μm and a thickness of between 0.7-5 μm.14. The ink jet print head according to claim 13, wherein each of thedriving electrodes has a width of between 80-200 μm and a thickness ofbetween 1-3 μm.
 15. The ink jet print head according to claim 7, whereinthe piezoelectric actuator has a flatness of 30 μm or less, which is adifference of height between projections and depressions formed on thepiezoelectric actuator at its surface to which the cavity plate isbonded.
 16. The ink jet print head according to claim 15, wherein theflatness is 30 μm less in an area of 5 mm².
 17. The ink jet print headaccording to claim 14, the piezoelectric actuator has the flatness of 30μm or less in an area of 5 mm².
 18. An ink jet print head, comprising: acavity plate that includes a plurality of nozzles and a plurality ofpressure chambers communicating with the respective nozzles; and aplate-like piezoelectric actuator formed into a single laminatedstructure by laminating a plurality of piezoelectric sheets including aplurality of electrodes which are formed at positions so as to bealigned with the respective pressure chambers, the laminatedpiezoelectric actuator sintered and bonded to the cavity plate so as toclose the pressure chambers provided in the cavity plate, wherein thepiezoelectric actuator has a flatness of 30 μm or less, which is adifference of height between projections and depressions formed on thepiezoelectric actuator at its surface to which the cavity plate isbonded.
 19. The ink jet print head according to claim 18, wherein theflatness is 30 μm or less in an area of 5 mm².
 20. A method offabricating an ink jet print head, comprising the steps of: forming acavity plate by laminating a plate, in which a plurality of nozzles areprovided, and a plurality of plates, in which a plurality of pressurechambers communicating with the respective nozzles are provided; forminga plate-like piezoelectric actuator by laminating a plurality ofpiezoelectric sheets, on each of which a plurality of driving electrodesare formed at positions with respect to the pressure chambers, and aplurality of piezoelectric sheets, on each of which a common electrodeis formed at a position to cover the pressure chambers; providingsurface electrodes, which electrically connect one of the drivingelectrodes and the common electrodes, at both end portions of a surfaceof the piezoelectric actuator, which is opposed to a surface to bebonded to the cavity plate; providing protrusions having a thickness ofthe surface electrodes, between the surface electrodes on the surface ofthe piezoelectric actuator; forming the piezoelectric actuator into asingle piece by sintering the piezoelectric actuator; and bonding thepiezoelectric actuator to the cavity plate so as to close the pressurechambers in the cavity plate while pressing both the surface electrodesand the protrusions using a jig having a flat surface.
 21. The method offabricating the ink jet head according to claim 20, wherein the surfaceelectrodes and the protrusions are printed on the surface of thepiezoelectric actuator at the same time using the same material.
 22. Themethod of fabricating the ink jet print head according to claim 21,wherein each of the piezoelectric sheets has a thickness of between15-30 μm.
 23. The method of fabricating the ink jet print head accordingto claim 22, wherein each of the driving electrodes has a width ofbetween 50-500 μm and a thickness of between 0.7-5 μm.
 24. The method offabricating the ink jet print head according to claim 22, wherein eachof the driving electrodes has a width of between 80-200 μm and athickness of between 1-3 μm.
 25. A method of fabricating a piezoelectricactuator for an ink jet print head, comprising the steps of: formingsheet-like members made of piezoelectric material; forming electrodepatterns on the sheet-like members; laminating the sheet-like members onwhich the electrode patterns are formed; placing the laminatedsheet-like members on a support member having a flat surface; andsintering the laminated sheet-like members on the support member,wherein a step of preventing adhesion of foreign substances to surfacesof the support member and the sheet-like members is provided both priorto and subsequent to the step of placing the laminated sheet-likemembers on the support plate and prior to the step of sintering thelaminated sheet-like members, so that the sheet-like member has aflatness of 30 μm or less, which is a difference of height betweenprojections and depressions formed on the sheet-like member at itssurface to which the cavity plate is bonded.
 26. The method offabricating the piezoelectric actuator for the ink jet print head,wherein the flatness is 30 μm or less in an area of 5 mm².
 27. Themethod of fabricating the piezoelectric actuator for the ink jet printhead, wherein each of the sheet-like member has a thickness of between15-30 μm.